It will be next to impossible to drill downward under the portion of the roof that slopes to the attic floor without a right angle drill.
How to drop ethernet from attic.
Poke some cable through one end more than you think you need and leave a short spool at the end slowly walk toward the other plate poke cable through done.
Attach the wire or cable to a fish tape or coat hanger using electrical tape and feed it into the hole until it reaches the opening at the other end.
My cable tv is distributed through the attic so it seemed like a good solution to run my home network through there as well.
If you re working from the attic you can drop a weighted string down wall cavity then attach the wire to the string and pull it through.
For single floor homes with a basement the basement may be the best path.
Depending on what the wiring is for this may be go through the drywall to the ceiling for instance for new lighting or be farther down on a wall.
Install brush plates go into attic preferably during a time when temperatures are tolerable walk to one end with your coiled cable in arm.